 /*
  * $Header: /cvshome/build/org.osgi.util.tracker/src/org/osgi/util/tracker/ServiceTrackerCustomizer.java,v 1.13 2007/02/19 19:04:33 hargrave Exp $
  *
  * Copyright (c) OSGi Alliance (2000, 2007). All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  * http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package org.osgi.util.tracker;

 import org.osgi.framework.ServiceReference;

 /**
  * The <code>ServiceTrackerCustomizer</code> interface allows a
  * <code>ServiceTracker</code> object to customize the service objects that
  * are tracked. The <code>ServiceTrackerCustomizer</code> object is called
  * when a service is being added to the <code>ServiceTracker</code> object.
  * The <code>ServiceTrackerCustomizer</code> can then return an object for the
  * tracked service. The <code>ServiceTrackerCustomizer</code> object is also
  * called when a tracked service is modified or has been removed from the
  * <code>ServiceTracker</code> object.
  *
  * <p>
  * The methods in this interface may be called as the result of a
  * <code>ServiceEvent</code> being received by a <code>ServiceTracker</code>
  * object. Since <code>ServiceEvent</code> s are synchronously delivered by
  * the Framework, it is highly recommended that implementations of these methods
  * do not register (<code>BundleContext.registerService</code>), modify (
  * <code>ServiceRegistration.setProperties</code>) or unregister (
  * <code>ServiceRegistration.unregister</code>) a service while being
  * synchronized on any object.
  *
  * <p>
  * The <code>ServiceTracker</code> class is thread-safe. It does not call a
  * <code>ServiceTrackerCustomizer</code> object while holding any locks.
  * <code>ServiceTrackerCustomizer</code> implementations must also be
  * thread-safe.
  *
  * @ThreadSafe
  * @version $Revision: 1.13 $
  */
 public interface ServiceTrackerCustomizer {
     /**
      * A service is being added to the <code>ServiceTracker</code> object.
      *
      * <p>
      * This method is called before a service which matched the search
      * parameters of the <code>ServiceTracker</code> object is added to it.
      * This method should return the service object to be tracked for this
      * <code>ServiceReference</code> object. The returned service object is
      * stored in the <code>ServiceTracker</code> object and is available from
      * the <code>getService</code> and <code>getServices</code> methods.
      *
      * @param reference Reference to service being added to the
      * <code>ServiceTracker</code> object.
      * @return The service object to be tracked for the
      * <code>ServiceReference</code> object or <code>null</code> if
      * the <code>ServiceReference</code> object should not be tracked.
      */
     public Object addingService(ServiceReference reference);

     /**
      * A service tracked by the <code>ServiceTracker</code> object has been
      * modified.
      *
      * <p>
      * This method is called when a service being tracked by the
      * <code>ServiceTracker</code> object has had it properties modified.
      *
      * @param reference Reference to service that has been modified.
      * @param service The service object for the modified service.
      */
     public void modifiedService(ServiceReference reference, Object service);

     /**
      * A service tracked by the <code>ServiceTracker</code> object has been
      * removed.
      *
      * <p>
      * This method is called after a service is no longer being tracked by the
      * <code>ServiceTracker</code> object.
      *
      * @param reference Reference to service that has been removed.
      * @param service The service object for the removed service.
      */
     public void removedService(ServiceReference reference, Object service);
 }

